Condensation, such as in the form of droplets on the interior surface of a lens of an enclosed lamp enclosure, for example, on the interior surface of a vehicle headlight, affects a lamp's function. Condensation can affect both a user's perception of lamp quality when the enclosure is in view, such as when a vehicle his parked and its headlamp is in view. Condensation can also affect photometric performance, undesirably refracting light. Condensation can be inhibited or condensate can be evaporated from a lens if the lamp enclosure is warm, but in some lamp enclosures, such as those using low heat-generating light sources, such as lamps that include light emitting diodes (LEDs), lamp operation may not generate enough heat at the lens to inhibit condensation or to clear condensate away.
Both active and passive approaches have been used in an attempt to reduce condensation in lamp enclosures. Active approaches can involve supplying electrical power to an electrical conductor that is in thermal contact with the enclosure to heat the enclosure. This approach can be expensive, at least because it relies on additional parts and manufacturing steps. Further, if the active element is part of the lens, it can affect photometric performance. Also, such an approach does not adequately address the problem of condensation in an unpowered car, where the vehicle is not actively heating the enclosure.
Passive approaches can include anti-fog agents or treatments applied on the interior surface of the lens to improve wetting, that is, to inhibit formation of small droplets and to thereby reduce light scattering. Such agents or treatments are designed to minimize the optical effects of condensation by favoring water films over water droplets; they are not designed to inhibit condensation on the lens, so there remains the potential for photometric variability according to environmental conditions. Moreover, additional manufacturing steps and costs are involved. Another passive approach is to design the lamp enclosure so as to direct the relatively low level of LED-generated heat to the lens, but this approach involves extra constraints on design.
An improved enclosure with a reduced propensity for condensation on selected surfaces of the enclosure is therefore desired.